Barwick

Like the title says. If I get an upgraded fuel pump, if it raises the fuel pressure, will that be enough to keep my engine properly fueled for, say, 10psi, maybe 11 psi? Only reason I ask is because it's ('90 TurboII) boosting to 5.5 psi right now because I THINK of clogged cats, so I'm going to get a full exhaust, but I don't REALLY care about the power gains right now, I just want to get it back up to the proper stock boost level.

Barwick

bump

scathcart

Nope.

When the fuel actually starts getting used at high rpms, the fuel pressure will drop back down to the stock 39 psi, thus eliminating any point to running higher then normal fuel presssures.

As well, if you can over-pressurize the stock FPR at idle, than you are going to run very rich and have lots of carbon build-up, as well as make very little.

Overall, this is a very bad idea. You **** with low-end power and don't even achieve the top-end results you were sacrificing the bottom end for.

If your fuel pump over-runs your FPR on the bottom end, get a aftermarket FPR. However, since the TII fuel pumps have a resistor pack, your fuel pump won't operate at full capacity on the bottom end unless you wire it to do so.

What are your fuel pump plans? 10psi is about as high as I recommend, and even that is a little high...

HAILERS

Time to show a touch of irritation. That remark that the fuel pressure would drop down to the stock 39psi is without a doubt.....well wrong.

I put a mechanical fuel gauge on my turboii. When I run boost the pressure RISES. It does not drop. I see close to 50 psi at 8psi boost. I have a stock fuel pressure regulator. And a stock fuel pump. The fuel pressure rises incrementaly as the boost goes up.

Ted challanged this remark. So I put two seperate fuel gauges on that same car and had the same results. For doubting Thomas's, put a mechanical fuel gauge inline with the rail. Put a MittyVac on the vac hose for the fuel pressure regulator. Increase the pressure at the fpr with the MittyVac. You'll see the fuel pressure RISE with an increase in pressure at the vac line(boost simulator).

If you have a fuel pressure gauge on your car and it stays at 39psi......I suggest you get your car fixed or the line to the fpr routed right where it sees boost pressure.

scathcart

Yeah, correct. Wasn't thinking of the boost factor. I can't watch my gauge under boost, seeing as it sits under the hood. However, mere forgetfulness need not form irritation.

I have a question: Do you run 42 psi fuel pressure under vacuum? I run an aftermarket FPR, and it is set at 40 psi until I start going into boost.

HAILERS

I had to go put the gauge back on and attach it to the wipers so I could go boost and look at it.

Start the car: 41psi for 55 seconds, then goes to 33psi.

Idle: 33 psi.

70 mph on a level road: 34/35 psi

Boot just a hair off 400 mm/hg : 48psi

NZConvertible

Linear rate FPR’s like ours always keep the difference between the fuel rail pressure and the manifold pressure constant. From Hailers’ figures this is about 40psi. So at idle, gauge pressure is ~16inHg (8psi) vacuum. Add 40psi and you get 32psi fuel pressure. With the engine off and the pump running, manifold pressure is zero so fuel pressure should be 40psi. At 8psi (420mmHg) boost fuel pressure should be 48psi.

RestoTII

so going back to the original question (cause I actually found this kind of interesting, but I'm interested in upgrading my pump too)... is it safe to upgrade the fuel pump and assume that the injectors may be dropping a little more fuel to make up for having intake, exhaust, and FCD? I can almost garauntee the answer will be "you need injectors, a S-AFC, gages, and a wideband O2 sensor", but I figured I'd give it a shot anyways.

Six Rotors

iTrader: (17)

Hey Hailers,I like the way you do things man!It sorts the bullshit from reality.The way some of these guys write I start to think they may not have an RX-7.

HAILERS

Sooooooo......now I think I know what is meant by a linear rate fpr. I'll catch on to some of this automobile mechanican someday by golly.

NZConvertible

As opposed to an aftermarket rising rate FPR, where instead of that constant 40psi, the difference between the manifold pressure and fuel pressure rises. This is why RRFPR's only enrich the top end.

Barwick

yeah, there's some sort of controller that only gives like 10 volts to the fuel pump under normal driving, and 12 volts under boost.. or something like that.. I forget.

But anyhow back to the original question, will this make up for added boost? Also will it be safe with the stock injectors to raise the pressure?

NZConvertible

It all depends on the pump you use. You will most probably be pushing a bit more fuel into the engine most of the time. The ECU's closed-loop operation will take care of this during cruise, but at idle and with any load you'll be running a bit richer than before. If your top-end was lean before it might fix this, but your mid-range might suffer because of this richness. Without dynoing it and logging the mixtures, you're just guessing. You don't need bigger injectors until you get close to 300hp, but a dyno-tuned S-AFC would take care of overly rich (or lean) mixtures.

Barwick

I heard around 250 flywheel hp, you're running >90% duty cycles on the stock injectors

NZConvertible

As long as adequate fuel pressure is maintained (the stock pump won't), four 550cc/min injectors can flow enough for 290-300hp at 80% duty.

jspecracer7

Jason's right on the money.

The ECU doesn't take into account Fuel pressure. It only knows that the injectors are this size, and that they're supposed to fire for this many milliseconds under this much air flow. So if you turn your fuel pressure up...well, you get the idea right?!

HAILERS

Not on the subject at hand, but thanks for the explanation or rising rate fpr vs the linear type in my car. I now understand why you would want a rising rate fpr to go with a Waldo fuel pump.

And just a note: When looking at the fuel pressure gauge on the wipers, and hitting boost, you can see when the fuel pump switches from the 10volts to the 12.5 volts. Its a jump of a couple or more psi. Forgot to note the exact amount or rise as that event happens, mainly because under boost it keeps a rising.

No disrespect meant to Scathcart in the earlier post.